Your safety: ONLY measure resistance with circuit DE-energised. You and your DMM don't like volts applied!!
The unit of resistance is Ohm, symbol Ω; 1000Ω= 1.00kΩ.
How does it work:
•The DMM feeds a small current through the circuit and calculates the resistance value.
•If circuit is open, DMM displays ‘1 ‘ or OL.
•If the resistance is 1.00kΩ, it’s displayed as 1.00
(there may be a kΩ sign in the display).
USE for LED testing:
- First select diode or continuity testing range on (rotary) selector (see DMM manual for details).
- Now touch probes together to get 0.00 display; you may get an audible indication as well.
- Then Open the probes to get ‘1 ‘ or OL.
- This proves the DMM is working correctly. Now test the LED as shown below.
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Testing a LED with DMM is simple through connecting the leads as shown.
Polarity is important! (Ignore displayed value on DMM)
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We'll assume the resistance value will be less than 2kΩ which is what you expect in lights.
- First select 2kΩ range on (rotary) selector (see DMM manual for details).
- Now touch probes together to get 0.00 display.
- Then Open the probes to get ‘1‘ or OL.
- This proves the DMM is working correctly. Now measure resistance; if display shows overload, select a higher range until a good reading is obtained (note if you select MΩ range, the circuit is open circuit). If display shows '.01', select a lower range to get better accuracy.
To measure the resistance of a string of light bulbs (2 examples):
HINT: instead of learning the standard banding codes for resistors (see below), just use the DMM to measure it. It's less error prone.
Note: when measuring high resistances above 50k Ohms, don't hold the resistor with your hands because your body resistance will lower the measured value, the displayed value is wrong. Your body has formed a parallel circuit to the resistor thereby lowering its displayed value.
NEXT >> Measuring current
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